Merge #10162: [trivial] Log calls to getblocktemplate

Summary:
1352092 Log calls to getblocktemplate (John Newbery)

Tree-SHA512: de2c6faac8baea2f63eb499dbcd0669062a71759050cf8bcada9b454fe82f056c23635d41c755badf55158ffc40a380f82bea1f40c8a2cc51604d981515b71eb

Backport of Core PR10162
https://github.com/bitcoin/bitcoin/pull/10162

Test Plan:

make check
test_runner.py mining_getblocktemplate_longpoll --nocleanup

Check /tmp/bitcoin_test_runner_*/mining_getblocktemplate_longpoll_82/node0/regtest/debug.log for a line similar to the following:

<date> <time> Received a POST request for / from 127.0.0.1:37080
<date> <time> ThreadRPCServer method=hgetblocktemplate

Reviewers: deadalnix, Fabien, jasonbcox, markblundeberg, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3383